1. Field
The field relates to a method of manufacturing an organic light emitting display, and more particularly, to a method of manufacturing an organic light emitting display including a thin film transistor (TFT) in which oxide semiconductor is used as an active layer and including a capacitor having a metal-oxide-semiconductor (MOS) structure, and a method of manufacturing the same.
2. Description of the Related Technology
In general, a thin film transistor (TFT) includes an active layer providing a channel region, a source region, and a drain region and a gate electrode insulated from the active layer of the channel region by a gate insulating layer.
The active layer of the TFT is made of a semiconductor such as amorphous silicon or poly-silicon. When the active layer is made of amorphous silicon, mobility is low so that it is difficult to realize a driving circuit driven at high speed. When the active layer is made of poly-silicon, since mobility is high but a threshold voltage is not uniform, a compensation circuit must be added.
In addition, it is difficult to apply a conventional TFT manufacturing method using low temperature poly-silicon (LTPS) to a large area substrate since a high-price process such as laser heat treatment is included and TFT characteristic control is difficult.
In order to solve the above-described problems, research on using an oxide semiconductor as the active layer have been recently performed.
In Japanese Patent Publication No. 2004-273614, a TFT in which an oxide semiconductor using zinc oxide (ZnO) as a main component is used as the active layer is disclosed.
The oxide semiconductor having ZnO used as the main component is estimated as an amorphous and stable material. When the oxide semiconductor is used as the active layer, the TFT may be manufactured by the conventional LTPS process at a low temperature no more than 300° C.
However, when the oxide semiconductor is used as the active layer, since the lower and upper electrodes of a capacitor are to be formed in the processes of forming the gate electrode and the source and drain electrodes of the TFT, the capacitor may be realized only by a metal-insulator-metal (MIM) structure. Since a thick insulating layer (inorganic material) is to be used as a dielectric material, it is difficult to realize high electrostatic capacity per a unit area. Therefore, in order to secure a uniform level of electrostatic capacity, the area of the capacitor is to be increased.